The gallery list rule is base on browser size(screen width or wrap width) and image self size. We use this plugin , there is not option to control list result. you have to change the image order, image size or remove image to change the list result

I think maybe there are different width window on Chrome and FF. Did you use same size browser width on Chrome and FF?

I did not resize the browser to get the gallery to disappear, it just seems to happen after being on the page for a while. I’ve only seen this happen in Chrome. (see attached za-galleryissue-chrome.jpg).